The present invention relates to modified diene polymer rubbers having an improved impact resilience, a low hardness at low temperatures and an improved processability. More particularly, the present invention relates to a process for preparing modified elastomeric polymers of conjugated diene compounds by introducing particular atomic groups to conjugated diene polymers, and a rubber composition containing the same.
Conjugated diene polymers such as polybutadiene and a styrene-butadiene copolymer have hitherto been used as rubbers for automobile tire treads. In recent years, from the viewpoint of demands in low fuel cost for automobiles and in running safety on snow and ice roads, rubber materials having a low rolling resistance and a large grip force on ice and snow roads have been desired as rubbers for automobile tire treads.
The rolling resistance is correlative to the impact resilience of polymers. The rolling resistance is decreased with increasing the impact resilience. On the other hand, it is known that the grip force on snow and ice roads is correlative to the hardness at low temperatures, and that the smaller the hardness at low temperatures, the larger the grip force on snow and ice roads. Known rubber materials are not satisfactory in these properties for practical use.
It was found that conjugated diene polymers having an increased impact resilience and a decreased low temperature hardness could be obtained when particular atomic groups were introduced to polymers by reacting alkali metal-containing diene polymers with particular compounds such as a nitro compound, a phosphoryl chloride compound, an aminosilane compound, an acrylamide compound and an aminovinylsilane compound. However, the conjugated diene polymers so modified by using the particular compounds have the defect detrimental to the practical use that they are poor in processability as represented by winding on roll.
It is an object of the present invention to provide a conjugated diene rubber having an improved processability as well as an improved impact resilience and a low hardness at low temperatures.
A further object of the present invention is to provide a process for modifying a conjugated diene polymer to improve the impact resilience and the processability and to lower the hardness under an atmosphere of low temperatures.
A still further object of the present invention is to provide a conjugated diene rubber composition having an improved processability and an improved storability and capable of providing a cured product improved in impact resilience and in hardness at low temperatures.
These and other objects of the present invention will become apparent from the description hereinafter.